This invention relates to a needle driving apparatus for a sewing machine, particularly to a needle driving apparatus for a sewing machine wherein a needle bar is allowed to move up and down through the oscillatory motion of an oscillating lever interlocking with a main shaft.
In such type of needle driving apparatus, while the oscillating lever performs an arcuate movement, the needle bar performs a linear movement. Accordingly, an element is required at the junction of said lever and needle bar for compensating the difference in their movements. Most of this type of prior art needle driving apparatus employ a slider element as an element for compensating said difference. However, the slider element induces greater inertia .force because of its relatively great mass, consequently, to bring about unfavorable influence upon the stitches to be formed. Also, since the slider element is provided on the side of the needle bar and the line of action of the force to be acted by the oscillating lever onto the needle bar is somewhat apart from the axis of the needle bar, a component of force is generated in the direction to increase the frictional resistance between said needle bar and a bearing which slidably supports the needle bar, in addition to the force to drive the needle bar to move along the axial direction thereof. As a result, the frictional resistance between the needle bar and the bearing will be increased, and thus these members will be worn very soon disadvantageously.
There has been proposed an apparatus wherein the oscillating lever and the needle bar are connected by means of a link as disclosed in U.S. Pat. No. 4,079,685. In this apparatus, when the oscillating lever oscillates, the link slants to right or left while allowing the needle bar to be moved up and down. However, with the change in the direction that the link slants, the line of action of the force to be acted upon the needle bar changes, thereby the needle bar is susceptible to wobbling. In order to make the vertical movement of the needle bar stable, the bearing for supporting the needle bar should be elongated; whereas if the bearing is elongated, the needle bar will naturally be longer. Moreover, in this apparatus a space for the link is required above the needle bar, and as a result a larger space is necessary for disposing the needle driving apparatus.
The object of this invention is to provide a needle driving apparatus for a sewing machine which has overcome the problems mentioned above.